Angular doesn't pass string variable to boolean expression

Question

I have an AngularJS function that uses JavaScript's RegExp() to look for a character at the start of a string. In this case, it's a lowercase p.

    $scope.checkState = function(state){
      var page = state;
      console.log(page);
      var regex = new RegExp("^[p]");
      var check = regex.exec(page);
      console.log('Regex evaluated to: ' + check);
      if (check == "p")
        return false;
      else
        return true;
    }

On the main HTML page, there is a button that is checking for an answer to the status of checkState(). If it returns as false, it hides the button from view with ng-show.

<md-button class="md-raised md-warn btn-right" ng-show="checkState({{pageID}})" ng-model="thing" ng-cloak onclick="thing()">My Button</md-button>

In here, pageID is a variable that contains a given ID value of a page template. When called in Angular, pageID becomes a string that is passed to the checkState() function.

Right now, I have been able to get the script to evaluate to null, but not to any other results. This is because despite the variable being filled in programatically, I get undefined instead.

What's going on here?

but you can simply do ng-show="checkState(pageID)" and that should work — harishr
– harishr, Commented Mar 28, 2016 at 16:12
Was just about to say, most any Angular directive will track these changes with each digest cycle. I don't know if that's the core problem, but it could be. — Harris
– Harris, Commented Mar 28, 2016 at 16:13

Thassa · Accepted Answer · 2016-03-28 16:18:49Z

2

Many thanks to @entre and @Harris Weinstein for their help. The problem was here:

ng-show="checkState({{pageID}})"

I had incorrectly thought that I needed to use the curly braces in order to get the string I needed. However, Angular doesn't need that when using its own function calls. Therefore, the correct way to pass the string is:

ng-show="checkState(pageID)"

answered Mar 28, 2016 at 16:18

Thassa

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